JPH07184069A - Confidential document management equipment - Google Patents

Abstract

PURPOSE:To decode a prescribed information code by visualizing a confidential document and embedding the code in a hard copy. CONSTITUTION:When a user 2 makes a request of a hard copy of a confidential document, a password request means 1 makes a request of a specific password to the user 2. A document image conversion means 4 uses a digital signal resulting from the password or a digital signal obtained by transforming of the password by a predetermined function as a key to convert an object document picture. An output means 7 outputs an image converted by the document image conversion means 4 as a copy. Furthermore, the document image conversion means 4 has an extract means 5 extracting a spatial frequency of an object document picture and an arithmetic means 6 converting a part of the spatial frequency extracted by the extract means 5 according to the given password.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a confidential document management apparatus, and more specifically, when visualizing a confidential document, a predetermined information code is embedded in a hard copy, and the embedded code is inserted as necessary. The present invention relates to a confidential document management device adapted to decrypt.

[0002]

2. Description of the Related Art Generally, the management of confidential documents requires the attention of the user. However, efforts are being made to increase safety. One of them is a method of making the document itself invisible to humans. The easiest way is to store it in the external memory of your computer or word processor. A floppy disk is a typical example. In order to visualize this, a specific operation by a specific device is required. In addition, as a conventional confidential document management method, one of the representatives requires the operator to input a specific password and validates that this password matches the one registered in advance or that it has a specific calculation relationship. It allows the visualization of confidential documents by treating them as unauthorized persons.

Previously proposed Japanese Patent Application No. 4-22523
No. 1 is equipped with a fixing device that fixes the transferred toner image and an identification code printing device that prints an identification code that identifies the copying machine using a color forming substance, and illegal copying is performed. The image forming apparatus is specified so that illegal copying can be suppressed and recidivism can be prevented. In addition, Japanese Patent Application No. 4
No. 239055 is a storage means in which a machine-specific identification mark is described, an identification mark synthesizing means for synthesizing image data with the identification mark stored in the storage means, and an image in which the identification mark is synthesized. The data is used as input data, and the dither pattern is switched between the identification mark composition portion and the other image data portion to perform dither processing so as to obtain the area gradation in the fine area. It is a feature of the image forming apparatus that has been broken, and makes it easy to suppress illegal copying and trace the criminal.

[0004]

As described above, the conventional confidential document management device is relatively easy to operate, and is thus inadequate from the viewpoint of maintaining confidentiality. Further, since the information once visualized can be freely copied, it becomes more difficult to manage the confidentiality. If multiple documents are visualized, it will be difficult to manage the confidential documents printed unless care is taken (for example, as handouts at a secret meeting). In order to reduce this worry, there is a "dense" mark that clearly indicates that it is a "confidential document", but there was a problem that there was no lump when it was copied.

The present invention has been made in view of the above circumstances, and when a confidential file is visualized, particularly when it is converted into a hard copy, the person who has made the copy during the hard copy, Providing a means to embed the purpose, date, etc., and later to be able to decipher this embedded code, and the embedded hard copy of the code is itself a normal document in appearance. Therefore, it is an object of the present invention to provide a confidential document management device in which reading and writing of this document are not restricted at all.

[0006]

In order to achieve the above object, the present invention provides (1) requesting means for requesting a specific password from a user who requests a hard copy of a confidential document, and the password or the password. A digital signal converted according to a certain function is used as a key, a conversion means for converting a target document image, and an output means for outputting the image converted by the conversion means as the copy, further, ( 2) The document image converting means has an extracting means for extracting a spatial frequency of a target document image and an arithmetic means for converting a part of the spatial frequency extracted by the extracting means according to a given password. ,
Further, (3) in (2), the run length of the target image is set to the spatial frequency, and
(4) In (3) above, only a specific run length value and a run length that is an integer multiple of the run length value are converted into another run length depending on the code string of the given password, and , (5) In the above (1),
Correcting the skew of the image in decoding the image, and (6) obtaining the frequency distribution from the image of the appropriate narrow region in (4), and distributing the narrow region,
The feature is that the code embedded in the image is decoded by checking whether or not the frequency characteristics of a wider area including the area are the same.

[0007]

When the user requests a hard copy of a confidential document, the user is requested to have a specific password. The target document image is converted using the password or the digital signal obtained by converting the password according to a certain function as a key, and the converted image is output as a copy. As the conversion of the document image, the spatial frequency of the target document image is extracted, and a part of the extracted spatial frequency is converted according to the given password.

[0008]

Embodiments will be described below with reference to the drawings. FIG. 1 is a block diagram for explaining an embodiment of a confidential document management apparatus according to the present invention. In the figure, 1 is a password requesting unit, 2 is a user, 3 is a confidential document storing unit, and 4 is a document image converting unit. Reference numeral 5 is extraction means, 6 is calculation means, and 7 is output means. When the user 2 requests a hard copy of a confidential document, the password requesting means 1 requests the user 2 for a specific password. The document image converting means 4 converts a target document image using a password or a digital signal obtained by converting the password according to a certain function as a key. The output unit 7 outputs the image converted by the document image conversion unit 4 as a copy. Further, the document image converting means 4 includes an extracting means 5 for extracting a spatial frequency of a target document image, and an arithmetic means for converting a part of the spatial frequency extracted by the extracting means according to a given password. Have

The present invention resides in converting an image into a frequency space and then processing the periodic distribution. The frequency space referred to here is the one obtained by orthogonally transforming the frequency space, for example, Fourier transform, or in the case of a text file, when the character code string is regarded as a one-dimensional chain of codes, the periodicity distribution of the code string is It is intended. The configuration of the invention will be specifically described below.

First, coding will be described. As an example, it is assumed that a binary image of white / black is given as shown in FIG. When an image is read in pixel units, it is often read in scan line units. That is,
A narrow range along a straight line is continuously read, and this signal is subdivided to form individual pixels. Consider the signal on this scan line in frequency space. The most frequently used frequency expression is the so-called run length distribution, which can be expressed as the distribution of the lengths of white and black continuous sections.

FIG. 2 shows an example of binarization. The scanning line starts from the upper left and reads in the horizontal direction. In the figure, 0 represents white pixels and 1 represents black pixels. The black run length distribution for the first 6 lines is shown in FIG. As you can see in the figure, there are many short runs. This distribution is characteristic of the document image, and if it is a document used for office work, it has a peak value in a short run and gradually declines to the right regardless of the language. Of course, when the number of samples is small, this gentleness cannot be expected.

The processing means will be described more specifically. Now, set the parameters used here as follows. s = 001100110010 (password code) N_code = 12 Run_one = 7, Run_zero = 5 N_repeat = 7 min_n_r = 5 In addition, the neighborhood includes one shorter than the set run length.

FIG. 4 is a flowchart of the entire processing of the confidential document management apparatus according to the present invention. Hereinafter, each step will be described in order. step1 ； Enter the password. The code of (operator + distributor) is set to s (code length is N_code bits). step2 : Insert a coding start signal in the output image. Read image: If there is no image to read, exit. step3 ; The number of black runs on the read scanning line: If n_r is larger than a certain value min_n_r, add 1 to n_line.
Otherwise do nothing. step4 ； Deform the run: If the bit of the n_line of the code s is 1, the run near the integral multiple of the run length Run_one is shortened. If the bit is 0, the run near the integral multiple of the run length Run_zero is shortened. To do. At the same time, the white run next to the shortened black run is lengthened by the length of the shortened black run. step5 ; When the operation of step 4 is repeated N_repeat times, 1 is added to the parameter n_step (n_step = n_li
ne / N_repeat) (However, the initial value of n_step is 0). step6 ; If n_step> N_code, reset n_step = 0 (to step 2).

That is, a start line that clearly indicates the start of processing is created in the output image. Since the target bit in the password is the 0th (that is, S (0) = 0) (n_step
= 0), the first four white pixels are out of scope and do nothing.
The next two black pixels are Run_one = 1 or Run_zero
Since it is less than = 1, nothing is done. The next white pixel column is also not processed and is not processed. Continuing the same process, the first black run targeted is the fourth black run (run length =
4). This is equal to Run_zero = 1, so change the run length to 3. At the same time, the next white run length 21 is changed to 22.

Similar processing is continued up to lines 1-7 in FIG. Since n_step = 1 on the 8th line, S
Check (1). Since S (1) = 0, the same processing as before is repeated. In the 12th and 13th scanning lines, the number of runs is 5
Therefore, ignore it. The 14 and 15 scan lines perform the same processing. The 16th line has n_step = 2, that is, S
(2) = 1, so the target black run length is a multiple of 7 and the value obtained by subtracting 1 from that value (6, 13, 20,
…) That is, the black run length is 6, 7, 1
If they match 3, 14, 20, 21, etc., they are changed to 5, 5, 12, 12, 19, 19, respectively, and the white run length that follows is corrected by the changed value.

The results are shown in FIG. As you can see in the figure, there is nothing wrong with the readability of the converted image. The black run length distribution for the first 6 lines in FIG. 5 is as shown in FIG. 6 (corresponding to code 0).
Looking at the distribution, it can be seen that the run length value is near zero in the vicinity of a multiple of 5, and the value immediately before that is large.

Next, the decoding will be described. So far, the procedure for embedding code information in an image has been described.
Next, restoring (decoding) the original embedded code information from the image transformed as described above will be described. FIG. 7 is a flowchart of a decryption process of the confidential document management device according to the present invention. Hereinafter, each step will be described in order. step1 : The image in which the digital code is embedded usually has a start mark. The start mark may be just one horizontal line, or may be another arrangement. If there is no mark, the manual instruction will be awaited. That is, the decoding start signal is searched (the image skew is corrected if necessary). if,
If it is found, the process proceeds to the following process. If not, the process waits for an input instruction.

[0018] step2; read an image on one scan line units. At this time, the input image is assumed to be binary of white / black. A scan line consists of thousands of pixels. If there is no image information, the process ends. step3 : The number of black runs in the scanning line read in step 2 is judged. That is, if there is little black information (here less than mim_n_r), do nothing.
Return to tep2. If not, move to the next step 4.

Step4 : First, the image to be read is usually slightly different from that when the image is plotted. This error is caused by the printing process of the printer and the sampling process when reading the image. Therefore, processing based on this error is performed below. When the value of n_line becomes N or more, the black run length distribution for the past N lines is set as hist_buff (r). When the value of n_line reaches N_repeat, the black run length distribution function up to that point is set as hist_current (f). Therefore, n_l
If ine> N, hist_buff (r) holds only the latest N lines.

[0020] step5; First of all, define the following function. f_current (j) = hist_current (X (j) -2) -hist_current
(X (j)) Similarly, f_prev (j) and f_buff (j) are defined. As is clear from the definition, this function is the difference between the frequency at the point X (j) and the frequency at the point X (j-2), and has a local peak when the difference between the two is large. . Further define the function:

[0021]

[Equation 1]

Similarly, period_buff (k) is also defined. The meaning of this function is the strength of periodicity in the sampling function k starting from the origin. By applying the equation (1) to the example of FIG. 6, a peak appears at k = 5. Of course, if the processed image of FIG. 5 is resampled by the scanner, the run length distribution function is also deformed, but (1)
If addition is made for a plurality of sections j as in the formula, the error becomes negligible. The inspection cycle k is
There are only two types, Run_one and Run_zero, and it is empirically known that the range of j that can be taken is 1 to 5, and therefore the number of calculations can be 10.

(1) n_line> N_repeat / 2 and period_buff (Run_one) = period_current (Run_one)>
Does N_peak hold? (2) n_line> N_repeat / 2 and period_buff (Run_zero) = period_current (Run_zero)
> Is N_peak valid? It should be noted that N_peak is a predetermined threshold value. If the condition (1) is satisfied, it means that the code 1 has been decoded, and the condition (2)
If is satisfied, 0 is decoded. If both do not hold, then it is undecipherable or unsuccessful, and if both hold, then the decryption is indeterminate. That is, the code is unknown.

Step 6 ; The codes decrypted in Step 5 are stored in order. Further, as shown in FIG. 7, the distribution function and parameters are reset. step7; bit string obtained by the step6 are generally classed as 8-bit units. This 8-bit unit is often used to represent alphanumeric characters. However, for alphanumeric characters, 7 bits is enough. The remaining 1 bit is used for error checking. That is, spare 1
Codes are assigned so that the total number of 1s is an even number or an odd number by combining bits and 7 bits for alphanumeric characters. With such a code string, the decoding code of step 6 can be easily error checked. Counts the number of 1's in a code string delimited by every 8 bits, and if it does not follow the predetermined even / odd rule, an error code (no explanation)
And output.

When decoding an image, there is a skew correction method. This skew correction method is described in "High-speed skew correction method for printed document image" (Koichi Ejiri, 3 persons, 1993,
The first meeting of the Institute of Image Electronics Engineers, p.45). With the advent of digital copiers, image information processing has entered the age of full-scale application, and for example, image information of a document is converted into a character code by OCR (character recognition) technology, which enables communication between a computer and a human. Came. Further, the efficiency of office work has been improved by automatically discriminating the type and nature of the document image and automatically cutting out the area. However, many of the techniques for skew correction have been developed because it is necessary to input an image without inclination (skew) as a prerequisite for these.

The input document image starts from a binary image in which the resolution is reduced to about 50 dpi. A pattern in which black pixels are connected is referred to as a "connected component" and is represented by a rectangle circumscribing the connected component. Now, assume that connected component rectangles are sequentially read from an A4 size document, and Buff_Size of them are stored in the Buffer memory. The left edges of some Buff_Size rectangles are horizontal if the column direction is horizontal,
If vertical, it is expected to line up vertically. Therefore, if the maximum value of the histogram of the coordinate values of one corner of a rectangle projected in both directions is taken, it is expected to represent the end point coordinates of the column. In this state, after another new rectangle "i" is read, the rectangle "i" is successively compared with the rectangle inside the buffer. If a rectangle "j" that meets the conditions shown in the pseudo program is found, its angle a (i, j)
Is calculated, and the histogram table hist_slope [a (i,
j)] is incremented by one. When the maximum value of hist_slope [a (i, j)] is calculated after performing the same processing on the entire image, the angle a (i, j) having this maximum value is the calculated skew angle.

[0027]

As is apparent from the above description, according to the present invention, a requesting means for requesting a specific password to a user requesting a hard copy of a confidential document and the password or the password according to a certain function. Management of printed confidential documents, since it has conversion means for converting the target document image by keying the converted digital signal and output means for outputting the image converted by the conversion means as a copy To facilitate.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of a confidential document management device according to the present invention.

FIG. 2 is a diagram showing an example of a binary image in the present invention.

FIG. 3 is a diagram showing a frequency distribution of black run lengths according to the present invention.

FIG. 4 is a flowchart of processing conditions of the confidential document management device according to the present invention.

FIG. 5 is a diagram showing a result of the processing in FIG.

FIG. 6 is a diagram showing a frequency distribution of black run lengths after deformation in the present invention.

FIG. 7 is a flowchart of a decryption process of the confidential document management device according to the present invention.

[Explanation of symbols]

1 ... Password requesting means, 2 ... User, 3 ... Confidential document storing means, 4 ... Document image converting means, 5 ... Extracting means, 6 ... Computing means, 7 ... Outputting means.

Claims (6)

[Claims] 1. A target document image is converted using request means for requesting a specific password from a user who requests a hard copy of a confidential document and a digital signal obtained by converting the password or the password according to a certain function as a key. A confidential document management apparatus, comprising: a conversion unit that performs the conversion, and an output unit that outputs the image converted by the conversion unit as the copy. 2. The document image converting means includes an extracting means for extracting a spatial frequency of a target document image, and an arithmetic means for converting a part of the spatial frequency extracted by the extracting means according to a given password. The confidential document management apparatus according to claim 1, further comprising: 3. The confidential document management apparatus according to claim 2, wherein the run length of the target image is the spatial frequency. 4. A specific run length value and a run length that is an integral multiple of the run length value are converted into another run length depending on a code string of a given password. Confidential document management device described. 5. The confidential document management apparatus according to claim 1, wherein skew of the image is corrected when the image is decoded. 6. A frequency distribution is obtained from an image of an appropriate narrow area, and it is checked whether or not the distribution of the narrow area and the frequency characteristic of a wider area including the area are the same.
5. The confidential document management device according to claim 4, wherein the code embedded in the image is decrypted.